The panel of the sequence disappears

It may help to first enable Window > Workspaces > Import Workspace from Project. This ensures the project’s saved workspace settings are available when you open it.

Otherwise, the number of Timeline panels shown depends on how many were displayed the last time that workspace was used. Even if a Timeline isn’t currently visible, it’s still open in the background—workspaces simply remember and update the number of Timeline tabs they display.

To fix this:

1. Create a custom workspace with the maximum number of Timelines you’ll need visible.
2. Go to Window > Workspaces > Reset to Saved Layout to refresh the workspace and make sure all open Timelines are displayed.

This is normal behavior in Premiere, it doesn’t reopen all sequences by default when you reload a project. Only the last few active ones stay open. If you want quick access, you can keep the rest saved in the Project Panel and just double-click to open them again.